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How Do You Calibrate Thermometer?


Full Member
Aug 13, 2002
Just got a new 2003 red Av and the thermometer is off by about 5 degrees celcius all the time (too high). I there a way to manually calibrate it if you know the temperature or does a dealer have to do this. Have any of you heard of this problem before. Other than that, the Av has been great and I especially like the Panasonic DVD player. :B:
I don't know but on the road yesterday my compass was going crazy. There was a word "CAL" on the mirror. The temp was not too far off but I was going north and it showed SW. I dropped it off at the dealer today for other things and they were going to fix it.
I don't know about the Temp, but I used the book to recalibrate my Compass. I had to hold both buttons or something and enter a digit on where I was in the US.

I think the temp may be off due to where the sensor is located. One day I almost died... it said the temp was 127 degree's. I was sitting still, and the sensor was reading the engine heat. When I started moving, everything went back to the correct temps.
Vehicle mounted thermometer are notoriously inaccurate. They sometimes read heat from the engine, heat rising off a dark road surface, etc. They are just there to give you an approximation of the outdoor temperature. When I was working as an electrician we used to install baseboard electric heat. One manufacturer got tired of customers complaining about the inaccuracy of their thermostats (has a lot to do with mounting position, height off the floor, etc., things the manufacturer could not control) that they replaced the degree numbers on the stat with a broad area that said "comfort zone". In other words, set the thing where you are comfortable and don't worry about the numbers. Perhaps that is good advice for our mirror mounted thermometers, accept them as an estimate and don't lose any sleep over a couple of degrees!
AV_Boy... The sensor location on the 2002 AV is behind the grill and almost always reads about 3-5 degrees F higher due to engine heat. I do not know if the sensor location is the same on the 2003. I have heard (can't remember where - maybe elsewhere in the forums) that some people have moved their sensors to a lower position to avoid the false temp reading.

Our thermometer was reading about 30 degrees F too low (-17 here in South TX). Dealer changed the sensor then finally the mirror to correct the problem. However, still have the 3-5 degree F variation from "real" temp.
Just_Jeepin said:
Our thermometer was reading about 30 degrees F too low (-17 here in South TX). ?Dealer changed the sensor then finally the mirror to correct the problem. ?However, still have the 3-5 degree F variation from "real" temp.
I would agree that 30 degrees too low is a problem, and should have been fixed, as it was.

I also agree with Big_Don that the temperature is an approximation at best, and being within 3 to 5 degrees sounds acceptable to me. Unless you get laboratory calibrated instrument, you will find that any thermometer can be off a few degrees.

As you said, the location of the sensor can cause it to pick up engine heat. This is particularly true when the engine is hot, and the truck is stopped or in stop and go traffic. When parked or stuck in a traffic jam, I have seen it rise 30 to 40 degrees above ambient. However, when travelling at steady highway speeds, it must have enough air flow over it that it settles down to be within a few degrees of actual. I'm happy with that, and I don't think it can be calibrated to do any better.

-- SS
When you see CAL on the compass...just drive in a circle a few times to reset it...this is in the manual I do believe......it happens occasional...but not a big deal....

If it happens all the time then check with dealer....

As for the thermometer......you have to compare it to an acurate thermoeter to know how much it is off.....I thinnk a few degrees is ok for me...over 10 and well I might want to check it.....but I would compare it to a high quality weather station type near the truck......and with the truck off and the engine cold.....
I have had the compass calibration come on on my old '02 Av. Just leave it calibrate itself and it is fine. The temp on the '02 Av also had the mirror-mounted thermometer but it was quite accurate. You guys speak of engine heat and such but that has never affected the thermometer on this Av or the last. Also, a thermostat is not meant to be entirely accurate for it is a lot harder to create an accurate analog thermostat than it is to perfect an electronic thermomter where the reading is the only pertinant outcome. Also the difference in temperature in degrees celcius is about a consistant 5 degrees and in farenheit is about 9 degrees. These readings were all taken in the winter when the engine was still fairly cold. Anyway, I'll have to go check the manual thanks for all your help. :B:
While I'll not complain about the temp reading while the Av is moving - just stop and watch the numbers climb. Here's another thread that discussed this - my eyes almost popped when ours read 142 degrees as we sat idling in a freeway jam . . .

High Temp Display Readings
Although you may be correct, I am speaking of temperature readings taken in -30 degrees celcius weather with barely any sun or heat from the engine. Up in Northern Ontario it does not get very hot for the sun to warm the thermometer over that of the actual temperature. It is like this in the night too. It is not that the temperature is fluctuating, it is 5 degrees (celcius) too high ALL THE TIME. Just wondering if it could be stepped down five degrees. (Just like a clock can be 5 minutes ahead while it still counts minutes and seconds accurately.) :B:
My thermometer is very accurate. Same in my Mercury. Just have to remember what it is measuring. If you are moving forward, you are measure the air temp about 3 feet above the pavement. If it is a windy cold/cool day, it should be accurate. If not, get it replaced. If it is a very hot no wind day, then the convection heat from the pavement will add a few degrees. At 80 degrees, it may add 1. At 85, 2. At 90, 3. Etc. The Av is less susceptible since the probe is higher than on a car. On my car I actually created a calibration chart to determine the "real" temp when it got over 80 degrees. And if you are sitting still, all bets are off since the engine heat is leaking forward.

I also had another vehicle where the probe could see the sun. Once i shaded it, it was accurate again.

I've noticed on cold days that my thermometer reads too high also, but after I start driving it corrects quickly.

Did these reading errors happen in the summer, or just the winter? After you have been driving for some time and the truck is warmed up, you still find the reading errors?

Av_boy, it's so darn cold up there in the "Great White North", why in the world would you want to know the temp!!?? ;),

At least set it for Farenheit, will seem warmer!